The grandiose mass in St Peter's Square to inaugurate Pope Francis, the new leader of the world's 1.2 billion Catholics, featured symbolic rituals and spectacular imagery.

Following are the main stages in the rare and historic event which lasted around two hours, attended by dozens of religious and world leaders as well as hundreds of thousands of pilgrims.

Tour of St Peter's Square

Francis, who was elected pope last week, left his temporary Vatican residence, Casa Santa Marta, around 8.45am local time (7.45 GMT). He began the day's events by greeting crowds in the piazza aboard an open vehicle.

Francis went into St Peter's Basilica, to the sacristy by Michelangelo's Pieta, to don his vestments for the mass. He stopped at the tomb of St Peter, regarded as the first pope, under the basilica's main altar.

The first Latin American pope was accompanied to the observance at the tomb by around 10 patriarchs and top archbishops of the Eastern Catholic Rite who co-celebrated the mass along with the other cardinals. Two key symbols of the papacy - the Fisherman's Ring and the pallium - as well as an ornate Bible had been placed at the tomb the night before.

The pallium - the same as that used for Francis's predecessor Benedict XVI - is a strip of wool worn over the shoulders recalling the role of Jesus as a good shepherd. Five red crosses on the vestment recall the wounds of the crucified Christ.

The Fisherman's Ring, made of gold-plated silver, bears the image of a bearded and haloed St Peter holding a pair of keys - representing the moment Peter was given the keys to heaven.

The ring originally served as both a symbol of the papacy and a seal, but these days the pope has a separate seal with which to mark documents.

Two leading cardinals carried the objects outside the basilica in a procession during which the prelates sang a special litany of saints titled Laudes Regi (Praises of the King).

Inauguration Mass

The mass was celebrated on the square outside - where tradition holds that Peter was crucified in around 67 AD.

At the altar in front of the basilica, Cardinal Jean-Louis Tauran bestowed the pallium on the pope, who then received the Fisherman's Ring from Cardinal Angelo Sodano.

A ritual followed in which six cardinals sweared their obedience to the pope on behalf of the three hierarchical levels of the College of Cardinals.

The mass was co-celebrated by around 180 clergymen including cardinals, patriarchs and archbishops and Adolfo Nicolas, the superior general of the Jesuit order to which Francis belongs.

The Vatican said about 250 bishops and archbishops were seated to the left of the altar along with clergy from other Christian churches.

More than 130 diplomatic delegations were seated on the right, while behind them were representatives of the Jewish, Muslim and other non-Christian faiths, followed by some 1,200 priests and seminarians.

The liturgy was that of St Joseph, the patron saint of the universal Church, whose feast day falls on Tuesday.

The gospel was sung in Greek only instead of both Greek and Latin as tradition normally dictates to embrace both Eastern and Western rites. Latin dominates many other parts of the mass.

The mass proper included a homily by Francis, who pledged that he would "embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important."

Music included "Tu Es Pastor Ovium" (Thou Art Shepherd of the Sheep), a rarely performed motet by Giovanni Pierluigi di Palestrina composed in 1585 for the enthronement of Sixtus V.